This invention relates to the field of data display modules and more particularly to an integral pocket clip and character display module that finds application in selective call personal paging receivers.
Selective call personal paging receivers ("pagers") can be categorized according to the method they use to convey a transmitted message to the user of the pager. "Tone only" pagers simply emit a short audible "alert tone" to inform the user that he or she has a message, but do not actually convey the message to the user. After hearing the alert tone, the user typically calls a prearranged telephone number to receive the actual message. "Tone and voice" pagers include the necessary audio circuits and a small speaker to permit the user to hear a verbal message following the alert tone. "Display" pagers include a small alphanumeric character display whereby a short message, such as a telephone number, may be displayed. One advantage of display pagers is that they convey the message silently, maintaining the user's message in confidence.
Recently developed paging systems transmit information from a base station to a paging receiver digitally. In a tone only system, a particular paging receiver is alerted by transmitting the pager's unique address code. In a display pager system, a message is sent to a particular paging receiver by transmitting the pager's unique address code followed by the message. A display pager uses the same basic circuits as a digital tone only pager, but additionally includes a display, display decoder circuitry, and circuitry or software to decode the message. Accordingly, to produce a display pager it is advantageous for a manufacturer to make a display module that attaches to its more basic line of tone only pagers. Therefore, by adding a display module with display decoder circuitry plus additional software or hardware to decode the message, the tone only pager can be upgraded to a display pager. This approach saves both development and manufacturing costs, and permits the manufacturer to introduce a display pager into its product line that is based on a proven product.
In the design of personal paging receivers, the trend has been towards reducing their overall size. With present technology, personal paging receivers are available that are sufficiently small and slim to fit into the user's shirt, blouse, or slacks pocket. Although a basic tone only "pocket" pager could be converted to a display pager by attaching a display module to the pager, this would undesirably increase the bulk of the pager in the user's pocket. Since pocket pagers typically have a pocket clip that holds the pager in the pocket by clamping the outer pocket material between the pager housing and the clip, it would be advantageous for the pager to have a display module built into the pocket clip, such that the additional bulk required for the display and decoder circuitry is added externally to the pocket.
Placing a display and decoder circuitry in the pocket clip, however, presents several problems. To begin, most displays are easily damaged by bending or twisting, therefore, the pocket clip housing must be sufficiently rigid to resist any deforming stresses, which are usually most severe during attachment and detachment of the pager to and from the pocket. The weight of the pocket pager, and consequently the weight of the pocket clip, is also important. Any additional weight increases the user's discomfort, especially when worn in a shirt or blouse pocket.
Creating the clamping pressure is also a problem when the display is included in the pocket clip. Because most displays are damaged by bending, the pocket clip cannot be constructed of flexible and resilient materials such that the clamping pressure is inherent in the clip itself. The display also increases the length of the pocket clip, especially where a large number of characters are displayed. If the clip were to be pivotally attached to the pager housing at the upper end of the clip, and a spring were positioned near the pivot point between the housing and the clip, well known principles of mechanics dictate that to maintain the same clamping pressure the spring tension must be increased proportionally with the length of the clip. Because of the space and weight requirements of pocket pagers, it is difficult to design a spring that can generate sufficient clamping force at the lower end of a long display pocket clip.